UPDATE m1
SET 
    membershipExpiration = m2.membershipExpiration, 
    welcomeKitLastSentOn = m2.welcomeKitLastSentOn,
    welcomeKitLastSentByFullName = m2.welcomeKitLastSentByFullName,
    needWelcomeKit = m2.needWelcomeKit,
    welcomeKitLastSentByUserId = m2.welcomeKitLastSentByUserId
FROM Memberships m1
INNER JOIN Memberships_20121014 m2 ON
    m1.membershipId = m2.membershipId
WHERE
    m2.membershipExpiration <> m1.membershipExpiration
